Digital-to-analog converters (DACs) are widely used for various applications such as audio, video, data conversion, etc. A DAC receives digital input data and provides an analog output signal. The performance of the DAC may be quantified by various dynamic specifications such as total harmonic distortion (THD), spurious free dynamic range (SFDR), signal-to-noise ratio (SNR), etc.
An N-bit DAC may be implemented with N binary weighted circuit elements, where a circuit element may be a current source, a capacitor, a resistor, etc. With binary weighting, the smallest circuit element has a size of one unit, the next smallest circuit element has a size of two units, and so on, and the largest circuit element has a size of 2N−1 units. In each sample period, zero or more of the N circuit elements may be selected based on a digital input data value and used to generate an analog output value for that sample period. The performance of the DAC is dependent on the accuracy of the sizes of the N binary weighted circuit elements. Since the size of the largest circuit element is 2N−1 times the size of the smallest circuit element, it may be difficult to accurately match these circuit elements. Consequently, the performance of the binary-weighted DAC may be relatively poor.
An N-bit DAC may also be implemented with 2N−1 circuit elements of equal size. In each sample period, a digital input data value of x may select x circuit elements to generate an analog output value for that sample period. Since all of the circuit elements have the same size, it may be easier to match these circuit elements. Nevertheless, there may be limitations on how closely the 2N−1 circuit elements can be matched. Hence, some mismatches typically exist between these circuit elements. To improve performance in the presence of the mismatches, the circuit elements may be selected in a manner such that errors due to the mismatches may be shaped and pushed out of band.
Accordingly, the present disclosure provides techniques to dynamically select circuit elements in order to mitigate deleterious effects due to circuit element mismatches.